brake bleeding problem with rear, MC bad?

[Swims350]

ok first up this is my 88 k1500, I REMOVED the RWAL dump valve. I did this by using a fitting that screws into the prop. valve and the line screws into it. Ok now trying to bleed the brakes, this is what's happening.

I bleed either side, starting on the PS rear of course but either one does this same thing..

bleed them once, works good, twice, still good, 3rd time, 4th. time any after barely get anything coming out and the pedal inside the truck moves less and less. The first time we'll say it moves halfway down, that's it, maybe more, 2nd time it'll only move 1/4 or less, 3rd. 1/8 or none and etc.

ok so I try to bleed them up front, at the prop. valve or at the MC. So this is what happens, pump the pedal and hold, crack the front line loose at either the MC or the Prop valve, fluid comes out, pedal travels all the way to the floor as it should.

crack the rear line loose at either the MC or the prop valve and the pedal moves only an inch or less, and does the same crap, 1st try an inch, 2nd try 1/2 3rd try nothing.

now bleeding the front brakes at the calipers the pedal will go all the way to the floor as it should.

one last thing, when the MC cover is off and you hit the pedal gently and watch it, the rear most part(for the front brakes) shoots up a stream of fluid as it should, the front tank(for the rear brakes) does nothing, no stream comes up or anything.


I think the master cylinder (MC) is shot, what do you think?

 

[badazzbulldog]

Open lh rear bleeder let it gravity bleed close once solid stream is coming out close do same on rh





Sent from my DROID X with true duals

 

[Swims350]

that may work but it seems like it's just not putting out any pressure and/or loosing pressure.

 

[badazzbulldog]

My thinking is its airbound try before getting new m/c

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[DGA1]

There is a chance that it is, because that does sound a bit weird. They are cheap and easy enough to replace that you might as well spend the $20-$30 and do it.

If you have not do these two things to test the booster and the MC just for kicks.
MC: with the truck on, step on the brake pedal and maintain pressure, if the pedal keeps sinking, the MC is bad.
Booster: with the truck off, pump up the pedal till firm. Afterward press the pedal and maintain pressure. If the pedal remains firm without sinking your booster is good.

 

[Swims350]

now it acts like it's clogged up. i had to gravity bleeding on the PS rear and it was doing good, almost sucked the MC dry, topped it off and couldn't get anything to come out. Finally got it going again, alot of bubbles,(have a foot long piece of clear tubing on the bleeder) then after awhile it stopped having anything, no bubbles, no fluid, and mc is full, cap is off the mc as well.

 

[Swims350]

the PS rear just stopped, nothing coming out. I popped on the mc lid and get some more air bubbles and fluid coming out, but then after maybe 20 seconds it stopped.

I can pump the pedal and it gets hard, it goes about halfway down and stops pretty much. Once I let up and then hit it, it travels to almost the floor, maybe 1/2 from the floor, engine not running.

 

[DGA1]

Yeah...I'd spend the money and replace it. Maybe it's throwing money at a problem, but I can not think of anything else but the MC. It's also cheap enough and if the thing is original and you plan on keeping the truck for a while, it's not a bad way to go.

 

[1997chevydriver]

Could also be the propvalve is turning off the pressure to the rear brakes. I had it happen once and i had to find a way to hold the little pin in the normal resting position to allow fluid to pass

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[Swims350]

that pin is it's normal resting place out or in?


ow for more testing..

took the lines off at the MC, hooked up the nipples you get to bleed them on the bench when you buy em, ran the tubes into the tanks, front hose front fitting on the MC to the front tank and so on.

At first the front did nothing. the back worked fully everytime.

the front started to work but only for the first half of the pedal travel, afterwards it stopped pumping, everytime.

The rear never stopped.

The rear also was squirting fluid up thru the tank from the bottom shooting up like a gyser(sp?) the front did not do this at all, anytime.

I'm pretty sure a good working MC squirts that way front and rear all the time when the lid is off. I can't really check though.

Also I can hear the fluid squirting inside the mc tank when we have the cap on and I never heard that before I don't think.



As for throwing money at it, I strongly think it may be worth it, $28 bucks for a reman, warranty, and if not then it's one less thing to fail later hopefully. I'm going to have my old man come check and help tomorrow, but may change it regardless and see what happens.

any advice is appreciated still.